The invention relates to a fan for a motor vehicle, especially for cooling the engine, comprising a stator and a rotor which is able to turn with respect to the stator about an axis in such a way as to produce an airflow in the direction of the said axis, the rotor and the stator respectively featuring blades and guide vanes which extend substantially radially into the said airflow, the guide vanes being situated downstream of the blades with respect to the airflow.
The rotor or impeller of an axial fan produces a substantially helical movement of the air, and the guide vanes have the function of straightening out this movement so as to make it parallel to the axis and thus to enhance the aerodynamic efficiency-of the fan.
The guide vanes used hitherto in motor-vehicle fans had an axial length, that is to say a dimension in the direction of the axis of rotation of the rotor, of the order of 20 mm, which was regarded as sufficient to ensure effective straightening of the airflow. However, new means of analysis have revealed that such was not the case, and that the known vanes were allowing a not inconsiderable circumferential component of the movement of the airflow to persist.
One aim of embodiments of the invention is to improve the geometric characteristics of the guide vanes in such a way as to obtain a practically perfect straightening of the airflow.
The invention especially envisages a fan of the type defined in the introduction, and provides for the axial length of the guide vanes to be equal to 40 mm at least.
Optional characteristics of the invention, which are complementary or alternative, are set out below:
the axial length of the guide vanes is equal to 60 mm at most. Beyond this value, the axial bulk of the stator increases without any benefit as regards the aerodynamic efficiency;
the acute angle xcexa9 between the chord of the flattened cross section of a vane and a radial plane lies between 25 and 35xc2x0;
the angle xcexa9 decreases progressively at least over the last 30% of the radial span of the vane;
the vanes have an aerodynamic camber lying between 1.5 and 2.5;
the vanes are produced in a single piece with a substantially annular central core from which they extend substantially radially outwards;
the vanes are produced in a single piece with an annular peripheral ring from which they extend substantially radially inwards;
the vanes are molded from a material chosen from a plastic and/or a magnesium-based material;
the stator and the rotor have an outer diameter lying between 200 and 500 mm;
the rotor is able to turn at a speed lying between 1500 and 4000 rpm.